A tapered roller bearing is used as a roller bearing for supporting a pinion shaft of a differential device additionally provided in a vehicle, or the like under a free rotation. The tapered roller bearing has a large load capacity, however, its rotation torque is large. Therefore, an oblique contact ball bearing (angular contact ball bearing) may be incorporated into the differential device or the like in place of the tapered roller bearing (for example, see the Patent Document 1), or an oblique contact double row ball bearing called a tandem double row ball bearing in which pitch circle diameters of double rows are different to each other, in other words, raceway diameters of the double rows are different to each other, may occasionally be incorporated into the differential device or the like.
The oblique contact double row ball bearing having the pitch circle diameters different to each other is effectively used particularly for the opinion shaft of the differential device or the like because the rotation torque thereof is smaller than that of the tapered roller bearing and the load capacity is sufficiently large.
In the case of incorporating these bearings into the differential device, the bearings are managed and stored in a state where a preload as prescribed is applied thereto.                Patent Document 1: No. 2003-156128 of the Japanese Patent Application Laid-Open        